The Piccadilly Theatre is a West End theatre located at 16 Denman Street, behind Piccadilly Circus and adjacent to the Regent Palace Hotel, in the City of Westminster, England. It was built in 1928 and is one of the largest theatres in London. The Piccadilly has presented most forms of stage entertainment and hosted some of the most famous faces in the business including Judi Dench, Ian McKellen and Barbara Dickson. Recent productions include Ghost the Musical, Jersey Boys and Annie. The sensational Moulin Rouge! The Musical comes to London’s Piccadilly Theatre from 12 November 2021 - and the West End has never seen anything like it. With 5 Drama Desk Awards, 11 Outer Critics Circle Awards, and 14 Tony Award Nominations including Best Musical, Best Director, and Best Choreography, this is a mash-up musical like no other.

Built by Bertie Crewe and Edward A. Stone for Edward Laurillard, its simple facade conceals a grandiose Art Deco interior designed by Marc-Henri Levy and Gaston Laverdet, with a 1,232-seat auditorium decorated in shades of pink. Gold and green are the dominant colours in the bars and foyer, which include the original light fittings. Upon its opening on 27 April 1928, the theatre's souvenir brochure claimed, "If all the bricks used in the building were laid in a straight line, they would stretch from London to Paris." The opening production, Jerome Kern's musical Blue Eyes, starred Evelyn Laye, one of the most acclaimed actresses of the period.

The Piccadilly was briefly taken over by Warner Brothers, and operated as a cinema using the Vitaphone system, and premièred the first talking picture to be shown in Great Britain, The Singing Fool with Al Jolson. The theatre reopened in November 1929, with a production of The Student Prince, having a success in January 1931 with Folly to be Wise, running for 257 performances.

The building sustained damage when it was hit by a stray German bomb during World War II.

In 1960, the Piccadilly was acquired by Donald Albery and became part of his group of London theatres. In the 1960s and 1970s, the Piccadilly improved its reputation with a series of successful transfers from Broadway: Who's Afraid of Virginia Woolf?, A Streetcar Named Desire and Man of La Mancha made their London debuts at the theatre. The Beatles recorded a number of songs at the Piccadilly on 28 February 1964 for the BBC Radio show, "From Us to You". In 1976, the Jerome Kern and Guy Bolton musical Very Good Eddie ran for 411 performances at the theatre. The cast included Prue Clarke.

In 1986, the venue was the setting for ITV's Sunday evening variety show, Live From the Piccadilly, hosted by Jimmy Tarbuck. The 1990s witnessed an expansion in ballet and dance, notably the most successful commercial ballet season ever to play in the West End, including Matthew Bourne's acclaimed production of Swan Lake.

The Piccadilly has played host to many famous stars such as Henry Fonda, Ian McKellen, Judi Dench, Michael Pennington, Barbara Dickson, Lynn Redgrave, Julia McKenzie, Eric Sykes, and Dame Edna. Its productions have run the gamut from Edward II to Spend Spend Spend to Noises Off to Blues in the Night to a season of plays directed by Sir Peter Hall.

The Donmar Warehouse production of Guys and Dolls ran at the Piccadilly from 19 May 2005 to 14 April 2007. It was followed by Paul Nicholas and David Ian's production of Grease which opened on 8 August 2007 and was the longest running show in the theatre's history before closing in April 2011 to make way for Ghost the Musical, which transferred to the Piccadilly in June 2011 following its world premiere at the Manchester Opera House.

On 6 November 2019 during an evening performance of Death of a Salesman, a section of plasterboard of the ceiling above the rear upper circle of theatre collapsed onto the audience with four people being taken to hospital. The incident was caused by a localised water leak. The local authority deemed the theatre safe to re-open two days later.